Engineer Kathleen Dunne’s prescription for supporting a shared rubblestone foundation wall called for a stepped reinforced buttress, sloped at the bottom to leave existing bearing soil undisturbed, and braced at the toe by the new basement slab at the lowered floor level.

Workers place and tie rebar for buttress sections in a Brooklyn basement as part of a project to lower the basement floor. The buttress will stabilize the basement wall, which is shared with an adjacent dwelling.

Workers assemble plywood forms in preparation for a concrete pour. The job was staged in order to maintain stability of the shared basement wall: end and center sections of the buttress were formed and placed first, then the center sections were excavated, formed, and poured.

Concrete flows into the stepped forms for a reinforcing buttress. The concrete will set in contact with the existing foundation structure and undisturbed site soils, maintaining the stability of a common party wall that supports the project house as well as a neighboring dwelling.

Concrete curing in the stepped forms for a reinforced buttress designed to stabilize a common basement foundation wall. Once the new buttress cures, remaining soil in the basement can be excavated and a new concrete slab will be placed to brace the toe of the buttress structure and provide a floor for the new, lowered basement living space.

This winter and spring, JLC will be following a gut-renovation and Passive House deep energy retrofit carried out on a typical Brooklyn, New York brick row house. Here’s our first look at the job, starting not with the energy details, but with the foundation work. Thousands of historic homes in New York City were built shoulder to shoulder along city blocks, sharing common rubblestone basement foundation walls, along with shared brick or stone party walls that support floor and roof framing. When one of those basements is deepened, the city requires underpinning, or some equivalent solution, to support adjacent structures. In this photo series from contractor Jose Maldonado and Passive House consultant Cramer Silkworth, we see the steps involved in shoring and buttressing an existing row house foundation so that the basement floor can be lowered.